There is a disk control unit that performs data reading and writing for plural disk drive units. A combination of the disk drive units and the disk control unit is referred to as a disk subsystem. Such a disk subsystem is disclosed in the Japanese Patent Application Laid-open No. 2001-228977.
Connection topology between a host computer and the disk subsystem are changing with technological backgrounds and users' needs. Generally, storage has been connected directly to a computer such as a host computer through an interface such as SCSI. Such storage is referred to as direct attached storage (DAS). In recent years, the amount of data processed by enterprises and general users has been continuing to increase explosively because of widespread use of electronic commerce and the use of applications using databases such as dataware house and multimedia data.
In the DAS connection mode, all requests arrive in storage via a host computer. Therefore, data backup and other operations heavily load the host computer and worsen response, and at the same time increase the load of a network such as LAN connecting the host computer, leading to the deterioration of the whole response. It becomes necessary to expand storage to provide for the explosive increase of data, which means that storage under control of a host computer must be individually expanded, requiring cumbersome operations.
From such a background, a storage area network (SAN) has emerged that connects a host computer and storage by a storage dedicated network different from a network such as LAN connecting host computer. Building the storage dedicated network provides merits such as lessening the load of a network connecting the host computer and speeding up a data backup operation. Also, since the storage can be managed in a centralized form, the system administrator is less loaded.
It is general to build SAN using fiber channels as an interface for building the system. Primarily, as the fiber channels, optical fiber cables connectable as far as tens of kilometers are used. Presently, the optical fiber cables provide a high-speed interface that provides a transfer speed of 2 Gbps and has higher performance than SCSI.
On the other hand, as disadvantages, initial installation costs are required to build a new network, a managerial load increases because of use of networks of two systems, and interoperability between fiber channel devices is not guaranteed.
Accordingly, attention is directed to SAN that can integrate networks of two systems and uses IP networks having many achievements in LAN and the like. In recent years, the explosive widespread use of the Internet and the emergence of gigabit Ethernet (Ethernet is a registered trademark) have rapidly promoted the prevalence, speedup, and band expansion of network infrastructure. Here, SAN using fiber channels and SAN using IP networks are differentiated as FC-SAN and IP-SAN, respectively.
iSCSI (Internet SCSI) is available as a protocol for accessing SCSI devices on the IP networks. iSCSI is a protocol for forwarding to IP networks TCP packets with unit packets called iSCSI PDU (iSCSP Protocol Data Unit) capsuled in a datagram portion thereof.
IP networking using iSCSI as a protocol for accessing SCSI devices are described in U.S. patent application Ser. No. 2002/0,029,281 A1, U.S. patent application Ser. No. 2002/0,083,120 A1 and U.S. patent application Ser. No. 2002/0,095,547 A1.
In conventional IP networking, devices connected to a network are computers such as a host computer, and communication with them is enabled in the Internet world after making a query to DNS (Domain Name Server) managing device names and addresses.
Since no storage devices have existed on IP networks heretobefore, storage devices cannot be managed with conventional DNS. Accordingly, iSNS (internet Storage Name Service) is proposed as the framework of IP storage device management.
iSNS is a protocol for managing computers such as a host computer and servers, and storage devices that exist on a certain network. In other words, the iSNS protocol can accommodate status changes such as addition and deletion of storage devices to and from the network, and addition of servers thereto.
However, with the iSNS, it is difficult to accommodate internal changes of the storage devices existing on the network.
For example, several thousands of disks are used in a large-scale disk subsystem designed for enterprises. The following function is achieved using the high-capacity disks: a copy of a certain data volume is created as a standby system within the identical disk subsystem, and when a failure occurs in a volume under normal operation, processing is switched to the standby system to continue the job, or the copied volume is assigned to a different job to perform parallel operation. For the copied volume, device information must be set to make it available to devices on the network. The volume is one that has been newly created within the disk subsystem, not newly created on the network. It means that the presence of the volume is unknown to devices on the network outside the disk subsystem, so that the above described function cannot be used.
Thus, although conventional storage management can accommodate status changes on the network, it cannot accommodate status changes such as data copy and data movement within storage.